Alzheimer's disease is associated with extensive loss of specific neuronal subpopulations in the brain (Sims, N. R., et al. (1987) Annals of Neuroloqy 21:451), with memory loss being the most universal symptom. (Katzman, R. (1986) New England Journal of Medicine 314:964). Alzheimer's disease has been linked to a genetic origin. (Schellenberg, G. D., et al. (1992) Science 258:668; Li, G., et al. (1991) Psychiatric Clinics of North America 14:267; St. George-Hyslop, P. H., et al. (1989) Neurobiology of Aging 10:417; St. George-Hyslop, P. H., et al. (1987) Science 235:885). Early-onset familial forms of the disease exhibit a genetic defect on chromosome 21. (St. George-Hyslop, P. H., et al. (1987)).
Cellular changes, leading to neuronal loss and the underlying etiology of the disease, remain unknown. Proposed causes include environmental factors, (Perl, D. P. (1985) Environmental Health Perspective 63:149; Katzman, R. (1986)), including metal toxicity, (Perl, D. P., et al. (1980) Science 208:297), defects in .beta.-amyloid protein metabolism, (Shoji, M., et al. (1992) Science 258:126; Joachim, C. L. and Selkoe, D. J. (1992) Alzheimer Disease Assoc. Disord. 6:7; Kosik, K. S. (1992) Science 256:780; Selkoe, D. J. (1991) Neuron 6:487; Hardy, H. and Allsop, D. (1991) Trends in Pharmacological Science 12:383), and abnormal calcium homeostasis and/or calcium activated kinases. (Mattson, M. P., et al. (1992) Journal of Neuroscience 12:376; Borden, L. A., et al. (1991) Neurobiology of Aging 13:33; Peterson, E., et al. (1989) Annals of New York Academy of Science 568:262; Peterson, C., et al. (1988) Neurobiology of Aging 9:261; Peterson, C., et al. (1986) Proceedings of the National Academy of Science 83:7999).
Alzheimer's disease is well characterized with regard to neuropathological changes. However, abnormalities have been reported in peripheral tissue supporting the possibility that Alzheimer's disease is a systemic disorder with pathology of the central nervous system being the most prominent. (Rizopoulos, E., et al. (1989) Neurobiology of Aging 10:717; Peterson (1986)).
Potassium channels have been found to change during memory storage. (Etcheberrigaray, R., et al. (1992) Proceeding of the National Academy of Science 89:7184; Sanchez-Andres, J. V. and Alkon, D. L. (1991) Journal of Neurobiology 65:796; Collin, C., et al. (1988) Biophysics Journal 55:955; Alkon, D. L., et al. (1985) Behavioral and Neural Bioloqy 44:278; Alkon, D. L. (1984) Science 226:1037). This observation, coupled with the almost universal symptom of memory loss in Alzheimer's patients, led to the investigation of potassium channel function as a possible site of Alzheimer's disease pathology and to the current invention.
The so-called patch clamp technique and improvements thereof, have been developed to study electrical currents in cells. The method is used to study ion transfer through channels. To measure these currents, the membrane of the cell is closely attached to the opening of the patch micropipette so that a very tight seal is achieved. This seal prevents current from leaking outside of the patch micropipette. The resulting high electrical resistance across the seal can be exploited to perform high resolution current measurements and apply voltages across the membrane. Different configurations of the patch clamp technique can be used. (Sakmann, B. and Neker, E. (1984) Annual Review of Physiology 46:455).
Currently, there is no laboratory diagnostic test for Alzheimer's disease. Therefore, there is a great need for a method to rapidly and clearly distinguish between Alzheimer's patients, normal aged people, and people suffering from other neurodegenerative diseases, such as Parkinson's, Huntington's chorea, Wernicke-Korsakoff or schizophrenia. Although some investigators have suggested that calcium imaging measurements in fibroblasts were of potential clinical use in diagnosing Alzheimer's disease (Peterson et al. 1986, 1988, supra), other researchers using similar cell lines and techniques, have shown no difference in calcium levels in Alzheimer's and normal control fibroblasts. (Borden et al. 1991, supra). Thus, the latter work refutes the findings of the former work.
The two proteins most consistently identified in the brains of patients with Alzheimer's disease have been .beta.--amyloid and tau, whose roles in the physiology or pathophysiology of brain cells are not fully understood. However, there has been no diagnostic nor prognostic laboratory tests for Alzheimer's disease involving these or other proteins. Further, few other proteins have been identified which have physiological implications for Alzheimer's disease.
The methods for diagnosing Alzheimer's disease of the present invention using cells isolated from patients are needed and will greatly improve the now very complicated clinical diagnostic process for Alzheimer's disease. These methods are especially important because they are able to distinguish patients with Alzheimer's disease from patients with other neurodegenerative diseases.